Lubricating oil composition for industrial machine, and lubricating method

ABSTRACT

A lubricating oil composition for industrial machines containing a base oil (A) and a specific acylglycerol (B) and having excellent brake squeal preventing performance, and a lubrication method using the composition.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition for industrial machines, and a lubrication method using the composition.

BACKGROUND ART

General industrial machines, for example, agricultural machines, construction machines and transporting machines are equipped with a transmission (gear), a hydraulically actuated part and the like, and a lubricating oil composition to be used in industrial machines is required to have viscosity characteristics for preventing seizure and wear of the transmission and for maintaining hydraulic output. In addition, these industrial machines are used for outdoor operation accompanied by high output power, and therefore the lubricating oil composition to be therein is desired to have stability against not only oxidation degradation but also heat and water.

Among industrial machines, for example, construction machines such as hydraulic power shovels, crane vehicles and bulldozers, and transporting machines such as dumper trucks, forklifts, shovel loaders and rough terrain haulers are further equipped with a wet brake, and the lubrication of the transmission (gear), the hydraulically actuated part and the wet brake that these machines have is generally a common lubrication in which they are lubricated with the same lubricating oil composition. For example, as the lubricating oil composition for these, a lubricating oil composition containing one or more selected from zinc dialkyldithiophosphates, basic calcium sulfonates and basic calcium phenates has been proposed (for example, see PTL 1).

CITATION LIST Patent Literature

PTL 1: JP 2009-144097 A

SUMMARY OF INVENTION Technical Problem

A problem peculiar to the wet brake is a repetition of sticking to and sliding on friction surfaces to occur between friction surfaces, that is, brake squeal caused by stick-slip oscillation or the like. Consequently, the lubricating oil composition to be used for industrial machines equipped with a wet brake is especially required to have also an ability to prevent brake squeal noises (hereinafter referred to as “brake squeal preventing performance”).

However, the lubricating oil composition disclosed in PTL 1 could not satisfy brake squeal preventing performance, and a lubricating oil composition capable of satisfying brake squeal preventing performance as well is desired.

The present invention has been made in consideration of the above-mentioned situation, and in particular, an object thereof is to provide a lubricating oil composition for industrial machines having excellent brake squeal preventing performance, and a lubrication method using the composition.

Solution to Problem

As a result of assiduous studies, the present inventors have found that the following invention can solve the above-mentioned problems. Specifically, the present invention provides a lubricating oil composition for industrial machines containing following constitutions and a lubrication method using the composition.

1. A lubricating oil composition for industrial machines, containing a base oil (A) and an acylglycerol (B) represented by the following general formula (1):

wherein R¹¹, R¹², and R¹³ each independently represent an acyl group represented by —C(═O)R¹⁴, or a hydrogen atom, at least any of R¹¹, R¹², and R¹³ is the acyl group, R¹⁴ represents a monovalent hydrocarbon group having 12 or more and 30 or less carbon atoms, and when a plurality of the acyl groups is present, R¹⁴'s in the acyl groups may be the same or different. 2. A lubrication method, including using the lubricating oil composition for industrial machines described in the above 1.

Advantageous Effects of Invention

According to the present invention, there can be especially provided a lubricating oil composition for industrial machines having excellent brake squeal preventing performance, and a lubrication method using the composition.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention (hereinafter also referred to as “this embodiment”) are described below. In this description, the numerical values relating to “or more” and “or less” regarding the description of the numerical value range may be combined in any manner.

[Lubricating Oil Composition]

The lubricating oil composition for industrial machines of this embodiment contains a base oil (A), and an acylglycerol (B) represented by the following general formula (1). Each component is described below.

In the general formula (1), R¹¹, R¹², and R¹³ each independently represent an acyl group represented by —C(═O)R¹⁴, or a hydrogen atom, and at least any of R¹¹, R¹², and R¹³ is the acyl group. R¹⁴ represents a monovalent hydrocarbon group having 12 or more and 30 or less carbon atoms, and when a plurality of the acyl groups is present, R¹⁴'s in the acyl groups may be the same or different.

(Base Oil (A))

The base oil (A) for use in the lubricating oil composition for industrial machines of this embodiment may be a mineral oil or a synthetic oil.

The mineral oil includes atmospheric residues obtained through atmospheric distillation of crude oils such as paraffin-base mineral oils, naphthene-base mineral oils or intermediate-base mineral oils; distillates obtained through reduced-pressure distillation of such atmospheric residues; mineral oils obtained by purifying the distillates through one or more purification treatments of solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing or hydrorefining, for example, light neutral oils, medium neutral oils, heavy neutral oils, and bright stocks; and mineral oils obtained by isomerizing wax produced through Fischer-Tropsch synthesis (GTL wax).

The mineral oil may be one grouped in any of Groups 1, 2 and 3 in the base oil category of API (American Petroleum Institute), but is, from the viewpoint of oxidation stability, preferably one grouped in Groups 2 and 3.

Examples of the synthetic oil include poly-α-olefins such as polybutenes, ethylene-α-olefin copolymers, and α-olefin homopolymers or copolymers; various esters such as polyol esters, dibasic acid esters, and phosphates; various ethers such as polyphenyl ethers; polyglycols; alkylbenzenes; and alkylnaphthalenes.

The viscosity of the base oil (A) is not specifically limited, but from the viewpoint of realizing an adequate viscosity of the lubricating oil composition for industrial machines, the kinematic viscosity at 40° C. thereof is preferably 20 mm²/s or more and 110 mm²/s or less, more preferably 23 mm²/s or more and 100 mm²/s or less, even more preferably 25 mm²/s or more and 95 mm²/s or less. The kinematic viscosity at 100° C. preferably falls within a range of 2 mm²/s or more and 25 mm²/s or less, more preferably within a range of 3 mm²/s or more and 20 mm²/s or less, even more preferably within a range of 5 mm²/s or more and 15 mm²/s or less.

The viscosity index of the base oil (A) is, from the viewpoint of realizing an adequate viscosity of the lubricating oil composition for industrial machines, preferably 80 or more, more preferably 90 or more, and even more preferably 95 or more. Here, the kinematic viscosity and the viscosity index are values measured according to JIS K 2283:2000 and using a glass-made capillary viscometer.

As the base oil (A), one kind of mineral oil may be used or two or more kinds thereof may be used in combination, or one kind of synthetic oil may be used or two or more kinds thereof may be used, or one or more kinds of mineral oil and one or more kinds of synthetic oil may be used in combination.

The content of the base oil (A) based on the total amount of the lubricating oil composition is, from the viewpoint of realizing an adequate viscosity of the lubricating oil composition for industrial machines, generally 50% by mass or more, preferably 60% by mass or more and 97% by mass or less, more preferably 70% by mass or more and 95% by mass or less, even more preferably 75% by mass or more and 93% by mass or less.

(Acylglycerol (B))

The lubricating oil composition for industrial machines of this embodiment contains an acylglycerol (B) represented by the following general formula (1).

In the general formula (1), R¹¹, R¹², and R¹³ each independently represent an acyl group represented by —C(═O)R¹⁴, or a hydrogen atom, and at least any of R¹¹, R¹², and R¹³ is the acyl group. R¹⁴ represents a monovalent hydrocarbon group having 12 or more and 30 or less carbon atoms, and when a plurality of the acyl groups is present, R¹⁴'s in the acyl groups may be the same or different. Here, when the carbon number of R¹⁴ is 11 or less, the solubility of acylglycerol (B) in the base oil lowers and the brake squeal preventing performance of the composition may lower. When the carbon number of R¹⁴ is 31 or more, the friction coefficient of the composition markedly lowers and the brake squeal preventing performance thereof may lower.

For example, the monovalent hydrocarbon group having 12 or more and 30 or less carbon atoms of R¹⁴ is preferably an aliphatic hydrocarbon group such as a linear or branched alkyl or alkenyl group having 12 or more and 30 or less carbon atoms, more preferably a linear or branched alkyl or alkenyl group having 12 or more and 24 or less carbon atoms, and even more preferably a linear or branched alkyl or alkenyl group having 16 or more and 20 or less carbon atoms. When R¹⁴ is an aliphatic hydrocarbon group having a carbon number mentioned above, the brake squeal preventing performance betters, and the solubility of the acylglycerol (B) in the base oil also betters and the friction coefficient of the composition increases.

Examples of the linear or branched alkyl group having 12 or more and 30 or less carbon atoms include various dodecyl groups such as a n-dodecyl group, an isododecyl group, a sec-dodecyl group, a tert-dodecyl group, and a neododecyl group (hereinafter hydrocarbon groups having a predetermined carbon number including linear and branched forms and also including isomers thereof may be abbreviated as various hydrocarbon groups), various tridecyl groups, various tetradecyl groups, various pentadecyl groups, various hexadecyl groups, various heptadecyl groups, various octadecyl groups, various nonadecyl groups, various eicosyl groups, various heneicosyl groups, various docosyl groups, various tricosyl groups, various tetracosyl groups, various pentacosyl groups, various hexacosyl groups, various heptacosyl groups, various octacosyl groups, various nonacosyl groups, and various triacontyl groups.

The linear or branched alkenyl group having 12 or more and 30 or less carbon atoms include various dodecenyl groups, various tridecenyl groups, various tetradecenyl groups, various pentadecenyl groups, various hexadecenyl groups, various heptadecenyl groups, various octadecenyl groups, various nonadecenyl groups, various eicosenyl groups, various heneicosenyl groups, various docosenyl groups, various tricosenyl groups, various tetracosenyl groups, various pentacosenyl groups, various hexacosenyl groups, various heptacosenyl groups, various octacosenyl groups, various nonacosenyl groups, and various triacontenyl groups.

Above all, in considering brake squeal preventing performance, alkyl groups having 16 or more and 18 or less carbon atoms such as various hexadecyl groups, various heptadecyl groups and various octadecyl groups, and alkenyl groups having 16 or more and 18 or less carbon atoms such as various hexadecenyl groups, various heptadecenyl groups and various octadecenyl groups are preferred; alkenyl groups having 16 or more and 18 or less carbon atoms such as various hexadecenyl groups, various heptadecenyl groups and various octadecenyl groups are more preferred; various heptadecenyl groups are even more preferred; and a n-heptadecenyl group is especially more preferred.

In this embodiment, at least any of R¹¹, R¹², and R¹³ is the acyl group. Specifically, the acylglycerol (B) may be a monoacylglycerol where any one of R¹, R¹², and R¹³ is an acyl group, or may be a diacylglycerol where any two of them are acyl groups, or may be a triacylglycerol where all the groups are acyl groups. The acylglycerol (B) is, from the viewpoint of brake squeal preventing performance, preferably a monoacylglycerol where any one of R¹¹, R¹², and R¹³ is an acyl group. In the case where the acylglycerol (B) is a monoacylglycerol or a diacylglycerol, R¹¹, R¹², and R¹³ that are not acyl groups among R¹¹, R¹², and R¹³ are preferably hydrogen atoms.

An especially preferred example of the acylglycerol (B) represented by the general formula (1) is a monoacylglycerol where any one of R¹¹, R¹², and R¹³ is an acyl group represented by —C(═O)R¹⁴, R¹⁴ is an alkyl or alkenyl group having 12 or more and 30 or less carbon atoms, and any two of the other R¹¹, R¹², and R¹³ are hydrogen atoms, more specifically a glycerin monooleate (of the general formula (1) where any one of R¹¹, R¹², and R¹³ is an acyl group where R¹⁴ is a heptadecenyl group and the others are hydrogen atoms), or a glycerin monostearate (of the general formula (1) where any one of R¹¹, R¹², and R¹³ is an acyl group where R¹⁴ is a heptadecyl group and the others are hydrogen atoms).

The content of the acylglycerol (B) based on the total amount of the composition is preferably 0.01% by mass or more and 2.5% by mass or less, more preferably 0.05% by mass or more and 1.5% by mass or less, and even more preferably 0.1% by mass or more and 1% by mass or less. When the content of the acylglycerol (B) falls within the above range, the brake squeal preventing performance and the solubility in base oil improve.

(Amine Compound (C))

Preferably, the lubricating oil composition of this embodiment further contains an amine compound (C) represented by the following general formula (2). The brake squeal preventing performance further improves.

In the general formula (2), R²¹ represents a hydrogen atom, or a monovalent hydrocarbon group having 12 or more and 30 or less carbon atoms, R²² and R²³ each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 or more and 5 or less carbon atoms, and at least one of R²¹, R²², and R²³ is a hydrocarbon group.

The monovalent hydrocarbon group having 1 or more and 30 or less carbon atoms of R²¹ is preferably an aliphatic hydrocarbon group such as a linear or branched alkyl or alkenyl group having 12 or more and 30 or less carbon atoms, more preferably a linear or branched alkyl or alkenyl group having 12 or more and 24 or less carbon atoms, even more preferably a linear or branched alkyl or alkenyl group having 16 or more and 20 or less carbon atoms. When the monovalent hydrocarbon group having 12 or more and 30 or less carbon atoms of R²¹ is an aliphatic hydrocarbon group having the above-mentioned carbon number, the brake squeal preventing performance improves. More specifically, regarding examples of the monovalent hydrocarbon group having 12 or more and 30 or less carbon atoms of R²¹, reference may be made to those exemplified for R¹⁴ in the acylglycerol (B) mentioned hereinabove.

Above all, in consideration of brake squeal preventing performance, alkyl groups having 16 or more and 18 or less carbon atoms such as various hexadecyl groups, various heptadecyl groups and various octadecyl groups, and alkenyl groups having 16 or more and 18 or less carbon atoms such as various hexadecenyl groups, various heptadecenyl groups and various octadecenyl groups are preferred; alkenyl groups having 16 or more and 18 or less carbon atoms such as various hexadecenyl groups, various heptadecenyl groups and various octadecenyl groups are more preferred; various octadecenyl groups are even more preferred; and a n-octadecenyl group is especially more preferred.

The monovalent hydrocarbon group having 1 or more and 5 or less carbon atoms of R²² and R²³ is, for example, preferably an aliphatic hydrocarbon group such as a linear or branched alkyl group having 1 or more and 5 or less carbon atoms, or a linear or branched alkenyl group having 2 or more and 5 or less carbon atoms, more preferably a linear or branched alkyl group having 1 or more and 3 or less carbon atoms, or a linear or branched alkenyl group having 2 or more and 3 or less carbon atoms, and even more preferably a linear alkyl group having 1 or more and 2 or less carbon atoms, or a linear alkenyl group having 2 carbon atoms. When R²² and R²³ each are an aliphatic hydrocarbon group having the above-mentioned carbon number, the brake squeal preventing performance improves and also the solubility of the amine in base oil also improves.

The linear or branched alkyl group having 1 or more and 5 or less carbon atoms includes a methyl group, an ethyl group, various propyl groups, various butyl groups and various pentyl groups. The linear or branched alkenyl group having 2 or more and 5 or less carbon atoms include a vinyl group, various propenyl groups, various butenyl groups and various pentenyl groups.

In this embodiment, at least any of R²¹, R²², and R²³ is a monovalent hydrocarbon group. Specifically, the amine compound (C) may be an amine where at least one of R²¹, R²², and R²³ is a hydrocarbon group (for example, monoalkylamine, monoalkenylamine), or may be an amine where any two of them each are a hydrocarbon group (for example, dialkylamine, dialkenylamine), or may be an amine where all of them each are a hydrocarbon group (for example, trialkylamine, trialkenylamine). The amine compound (C) is, from the viewpoint of the brake squeal preventing performance, preferably an amine where any one of R²¹, R²², and R²³ is a hydrocarbon group.

Especially preferred compounds of the amine compound (C) represented by the general formula (2) are monoalkylamines or monoalkenylamines where R²¹ is an alkyl or alkenyl group having 12 or more and 30 or less carbon atoms, and R²² and R²³ are hydrogen atoms, more specifically, monostearylamines (of the general formula (2) where R²¹ is an octadecyl group and R²² and R²³ are hydrogen atoms), or monooleylamines (of the general formula (2) where R²¹ is an octadecenyl group and R²² and R²³ are hydrogen atoms).

The content of the amine compound (C) based on the total amount of the composition is preferably 0.01% by mass or more and 2.5% by mass or less, more preferably 0.05% by mass or more and 1.5% by mass or less, and even more preferably 0.1% by mass or more and 1% by mass or less. When the content of the amine compound (C) falls within the above range, the brake squeal preventing performance and also the solubility in base oil may improve. From the same viewpoint, the nitrogen atom content in the amine compound (C) based on the total amount of the composition is preferably 3 ppm by mass or more and 1,200 ppm by mass or less, more preferably 20 ppm by mass or more and 750 ppm by mass or less, and even more preferably 45 ppm by mass or more and 450 ppm by mass or less.

(Other Additives)

In the lubricating oil composition of the present invention, within a range not detracting from the object of the present invention, any other additives than the base oil (A) and the acylglycerol (B) and the optional component, amine compound (C), for example, any other additives such as a viscosity index improver, a pour point depressant, an anti-foaming agent, an anti-wear agent, an extreme pressure agent, a metal-based detergent, a dispersant, an antioxidant, an oiliness agent, a friction modifier, a metal deactivator and a rust inhibitor may be suitably selected and blended therein. One alone of these additives may be used or plural kinds thereof may be used in combination. The lubricating oil composition of the present invention may be composed of the above-mentioned base oil (A) and the acylglycerol (B), or may be composed of the base oil (A), the acylglycerol (B) and the amine compound (C), or may be composed of the base oil (A), the acylglycerol (B), the amine compound (C) and other additives.

The total content of the other additives is not specifically limited so far as it does not detract from the object of the present invention. However, considering the effect of the addition of the other additives, the total content of the other additives is preferably 0.1% by mass or more and 25% by mass or less based on the total amount of the composition, more preferably 1% by mass or more and 20% by mass or less, even more preferably 5% by mass or more and 18% by mass or less.

(Viscosity Index Improver)

The lubricating oil composition of the present invention may contain, for the purpose of improving the viscosity index of the base oil (A), a viscosity index improver. Examples of the viscosity index improver include polymers such as a non-dispersant-type polymethacrylate, a dispersant-type polymethacrylate, an olefin-based copolymer (for example, an ethylene-propylene copolymer), a dispersant-type olefin-based copolymer, and a styrene-based copolymer (for example, a styrene-diene copolymer, a styrene-isoprene copolymer).

The mass-average molecular weight (Mw) of the viscosity index improver may be suitably determined depending on the kind thereof, but is, from the viewpoint of viscosity characteristics, generally 500 or more and 1,000,000 or less, preferably 5,000 or more and 800,000 or less, more preferably 10,000 or more and 600,000 or less.

In the case of a non-dispersant-type or dispersant-type polymethacrylate, the mass-average molecular weight thereof is preferably 5,000 or more and 1,000,000 or less, more preferably 10,000 or more and 800,000 or less, and further more preferably 20,000 or more and 600,000 or less. In the case of an olefin-based copolymer, the mass-average molecular weight thereof is preferably 800 or more and 300,000 or less, more preferably 1,000 or more and 250,000 or less, even more preferably 10,000 or more and 200,000 or less.

Here, the mass-average molecular weight is obtained from the calibration curve drawn by using polystyrene through measurement of gel permeation chromatography (GPC). For example, the mass-average molecular weight of each polymer mentioned above may be calculated as the value converted in terms of polystyrene according to the GPC method mentioned below.

<GPC Measuring Apparatus> Column: TOSO GMHHR-H(S)HT

Detector: RI detector for liquid chromatography, WATERS 150C

<Measurement Condition, Etc.>

Solvent: 1,2,4-trichlorobenzene Measurement temperature: 145° C. Flow rate: 1.0 mL/min Sample concentration: 2.2 mg/mL Injection amount: 160 μL Calibration curve: Universal Calibration Analysis program: HT-GPC (Ver. 1.0)

The content of the viscosity index improver is, from the viewpoint of viscosity characteristics, preferably 0.5% by mass or more and 15% by mass or less based on the total amount of the composition, more preferably 1% by mass or more and 10% by mass or less, even more preferably 1.5% by mass or more and 5% by mass or less.

(Pour Point Depressant)

Examples of the pour point depressant include ethylene-vinyl acetate copolymers, condensation products of chloroparaffin and naphthalene, condensation products of chloroparaffin and phenol, polymethacrylates, and polyalkylstyrenes.

(Anti-Foaming Agent)

Examples of the anti-foaming agent include silicone oils, fluorosilicone oils, and fluoroalkyl ethers.

(Anti-Wear Agent)

Examples of the anti-wear agent include sulfur-containing compounds such as zinc dialkyldithiophosphates (ZnDTP), zinc phosphate, zinc dithiocarbamate, molybdenum dithiocarbamate, molybdenum dithiophosphate, disulfides, sulfurized olefins, sulfurized oils and fats, sulfurized esters, thiocarbonates, thiocarbamates, and polysulfides; phosphorus-containing compounds such as phosphites, phosphates, phosphonates and amine salts or metal salts thereof, and sulfur and phosphorus-containing anti-wear agents such as thiophosphites, thiophosphates, thiophosphonates, and amine salt or metal salts thereof.

(Extreme Pressure Agent)

Examples of the extreme pressure agent include sulfur-containing extreme pressure agents such as sulfides, sulfoxides, sulfones and thiophosphinates; halogen-containing extreme pressure agents such as chlorohydrocarbons; and organic metal-containing extreme pressure agents.

(Metal-Based Detergent)

Examples of the metal-based detergent include neutral metal sulfonates, neutral metal phenates, neutral metal salicylates, neutral metal phosphonates, basic metal sulfonates, basic metal phenates, basic metal salicylates, basic phosphonates, overbased metal sulfonates, overbased metal phenates, overbased metal salicylates, and overbased phosphonates, of alkaline earth metal such as calcium.

(Dispersant)

Examples of the dispersant include ash-free dispersants such as boron-free succinimides, boron-containing succinimides, benzylamines, boron-containing benzylamines, succinates, and mono or dicarboxylic acid amides of typically fatty acids or succinic acid.

(Antioxidant)

Examples of the antioxidant include amine-based antioxidants such as diphenylamine-based antioxidants, and naphthylamine-based antioxidants; phenol-based antioxidants such as monophenol-based antioxidants, diphenol-based antioxidants, and hindered phenol-based antioxidants; molybdenum-based antioxidants such as molybdenum amine complexes produced by reacting molybdenum trioxide and/or molybdic acid and an amine compound; sulfur-based antioxidants such as phenothiazine, dioctadecyl sulfide, dilauryl-3,3′-thiodipropionate, and 2-mercaptobenzimidazole; and phosphorus-based antioxidants such as triphenyl phosphite, diisopropylmonophenyl phosphite, and monobutyldiphenyl phosphite.

(Oiliness Agent)

Examples of the oiliness agent include aliphatic monocarboxylic acids such as stearic acid and oleic acid; polymer fatty acids such as dimer acids and hydrogenated dimers; hydroxyfatty acids such as ricinoleic acid and hydroxystearic acid; aliphatic monoalcohols such as lauryl alcohol and oleyl alcohol; fatty acid amides such as lauric acid amide and oleic acid amide.

(Friction Modifier)

Examples of the friction modifier include ash-free friction modifiers such as fatty acid amines, fatty acid esters, fatty acid amides, fatty acids, aliphatic alcohols and fatty acid ethers having at least one alkyl group or alkenyl group having 6 or more and 30 or less carbon atoms, especially a linear alkyl or alkenyl group having 6 or more and 30 or less carbon atoms in the molecule; and molybdenum-based friction modifiers such as molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDTP), and molybdic acid amine salts.

(Metal Deactivator)

The metal deactivator include benzotriazole compounds, tolyltriazole compounds, thiadiazole compounds and imidazole compounds.

(Rust Inhibitor)

Examples of the rust inhibitor include petroleum sulfonates, alkylbenzene sulfonates, dinonylnaphthalene sulfonates, alkenylsuccinates, and polyalcohol esters.

(Various Physical Properties of Lubricating Oil Composition)

In the lubricating oil composition for industrial machines of this embodiment, the total nitrogen atom content based on the total amount of the composition is preferably 500 ppm by mass or more and 2,000 ppm by mass or less, more preferably 550 ppm by mass or more and 1,750 ppm by mass or less, even more preferably 600 ppm by mass or more and 1,500 ppm by mass or less. When the total nitrogen atom content falls within the above range, brake squeal preventing performance improves.

The lubricating oil composition for industrial machines of this embodiment preferably has a ratio of a kinematic friction coefficient (μ₀) to a kinematic friction coefficient (μ_(d)) (μ₀/μ_(d), hereinafter referred to as a friction coefficient ratio) of 1 or less. The kinematic friction coefficient (μ₀) and the kinematic friction coefficient (μ_(d)) are measured after 1 cycle, 100 cycles, 500 cycles, 1,000 cycles, 3,000 cycles and 5,000 cycles respectively in a kinematic friction test according to JASO M348:2002 (test method for friction characteristics of automatic transmissions) using SAE No. 2 friction tester. When the friction coefficient ratio in the kinematic friction test (after 1 cycle, after 100 cycles, after 500 cycles, after 1,000 cycles, after 3,000 cycles, and after 5,000 cycles) is 1 or less, the brake squeal preventing performance can be expressed from the initial stage and for a long period of time. Here, the kinematic friction test is according to the method described in the section of Examples. From the same viewpoint as above, the friction coefficient ratio is more preferably less than 1, and even more preferably 0.99 or less.

The kinematic viscosity at 40° C. of the lubricating oil composition for industrial machines of this embodiment is preferably 30 mm²/s or more and 70 mm²/s or less, more preferably 35 mm²/s or more and 65 mm²/s or less, even more preferably 40 mm²/s or more and 60 mm²/s or less. The kinematic viscosity at 100° C. is preferably 7 mm²/s or more and 12 mm²/s or less, more preferably 8 mm²/s or more and 11 mm²/s or less, even more preferably 8.5 mm²/s or more and 10 mm²/s or less.

The viscosity index of the lubricating oil composition for industrial machines of this embodiment is preferably 130 or more, more preferably 135 or more, and even more preferably 140 or more.

Here, the method for measuring the kinematic viscosity and the viscosity index is the same as that for the base oil mentioned hereinabove.

[Lubrication Method]

The lubrication method of this embodiment is a lubrication method including using the lubricating oil composition for industrial machines of this embodiment described above. The lubricating oil composition for industrial machines for use in the lubrication method of this embodiment has especially excellent brake squeal preventing performance, and is also excellent in other performance required for lubricating oil compositions for general industrial machines, for example, in transmission seizure and wear preventing performance, in viscosity characteristics and in stability against oxidation degradation.

Accordingly, the lubrication method of this embodiment exhibits an excellent effect in general industrial machines such as agricultural machines, construction machines and transporting machines equipped with a transmission (gear), a hydraulically actuated part and the like. In particular, in the case of common lubrication for industrial machines equipped with a transmission (gear), a hydraulically actuated part and a wet brake, for example, construction machines such as hydraulic power shovels, crane vehicles and bulldozers, and transporting machines such as dumper trucks, forklifts, shovel loaders and rough terrain haulers, the lubricating oil composition of the present invention can effectively exhibit the brake squeal preventing performance.

EXAMPLES

Next, the present invention is described in more detail with reference to Examples, but the present invention is not limited at all by these Examples.

Examples 1 and 2, and Comparative Example 1

Lubricating oil compositions were prepared at the blending ratio (% by mass) shown in Table 1. Regarding the resultant lubricating oil compositions, various test were conducted according to the methods mentioned below to evaluate the properties thereof. The evaluation results are shown in Table 1. Details of the components shown in Table 1 used in these Examples are as follows.

Base oil 1: 150 N (neutral) hydrogenated pure mineral oil, 40° C. kinematic viscosity: 29.6 mm²/s, 100° C. kinematic viscosity: 5.37 mm²/s, viscosity index 116, API Group 2. Base oil 2: 500 N (neutral) hydrogenated pure mineral oil, 40° C. kinematic viscosity: 91.5 mm²/s, 100° C. kinematic viscosity: 10.5 mm²/s, viscosity index 96, API Group 2. Acylglycerol (B): glycerin monooleate (monoacylglycerol of general formula (1) where R¹¹ is —C(═O)R¹⁴ (R¹⁴ is n-heptadecenyl group), R¹² and R¹³ are hydrogen atoms. Amine compound (C): monooleylamine (general formula (2) where R²¹ is a n-octadecenyl group, and R²² and R²³ are hydrogen atoms), nitrogen atom content: 5.2% by mass. Viscosity index improver: polymethacrylate, mass-average molecular weight: 35,000. Other additives: pour point depressant, anti-foaming agent, anti-wear agent (zinc dialkyldithiophosphate (ZnDTP)), metal-based detergent, oiliness agent (oleic acid amide), amine-based antioxidant.

The properties of the lubricating oil compositions were measured and evaluated according to the methods mentioned below.

(1) Kinematic Viscosity

Kinematic viscosity at 40° C. and 100° C. was measured according to JIS K 2283:2000.

(2) Viscosity Index (VI)

Measured according to JIS K 2283:2000.

(3) Content of Nitrogen Atom

Measured according to JIS K 2609:1998.

(4) Calculation of kinematic friction coefficient (μ₀), kinematic friction coefficient (μ_(d)), and friction coefficient ratio (μ₀/μ_(d)) in kinematic friction test

The lubricating oil compositions of Examples and Comparative Examples were tested according to the following kinematic friction test to calculate the kinematic friction coefficient (μ₀), the kinematic friction coefficient (μ_(d)), and the friction coefficient ratio (μ₀/μ_(d)) thereof.

(Kinematic friction test: friction test according to JASO M348:2002 (test method for friction characteristics of automatic transmissions) using SAE No. 2 friction tester)

Using SAE No. 2 friction tester, the lubricating oil compositions were tested in a kinematic friction test under the conditions mentioned below to measure various friction torques (T_(d), T₀) at a rotational frequency (500 rpm) for calculation of the kinematic friction coefficient (μ_(d)) and at a rotational frequency (200 rpm) for calculation of the kinematic friction coefficient (μ₀), and the kinematic friction coefficient (μ_(d), μ₀) at the corresponding friction torque was calculated according to the following mathematical expression (1), and the friction coefficient ratio (μ₀/μ_(d)) was then calculated.

$\begin{matrix} {µ = \frac{T}{2 \times n \times {re} \times P \times A}} & (1) \end{matrix}$

μ: kinematic friction coefficient

T: friction torque (Nm)

n: number of friction discs (3)

re: mean friction effective radius (66.4 mm)

P: pressing load (298 kPa)

A: friction area (57.40 mm²)

(Test Conditions)

Assemblage of friction materials: steel plates (4)/paper discs (3) Moment of inertia of inertial disc: 0.725 kg·m² Test rotational frequency: 800 rpm Rotation rising time: 8±2 seconds Oil temperature: 90° C. Oil amount: 700 mL Friction plate surface pressure: 785 kPa Test cycle: 30 sec/cycle Pressing load rising time: 0.1 to 0.15 seconds Pressing load retention time: 2 seconds Test cycles: one cycle, 100 cycles, 500 cycles, 1000 cycles, 3000 cycles or 5000 cycles Rotational frequency for calculation of kinematic friction coefficient (μ_(d)): 500 rpm Rotational frequency for calculation of kinematic friction coefficient (μ₀): 200 rpm

TABLE 1 Comparative Example Example 1 2 1 Base Oil 1 (mass %) 72.0 72.0 72.0 Base Oil 2 (mass %) 11.0 10.5 11.5 Acylglyerol (B) (mass %) 0.5 0.5 0.0 Amine Compound (C) (mass %) 0.0 0.5 0.0 Viscosity Index Improver (mass %) 3.6 3.6 3.6 Other Additives (mass %) 12.9 12.9 12.9 Total (mass %) 100.0 100.0 100.0 Total nitrogen content (ppm by mass) 760 1020 750  40° C. Kinematic Viscosity (mm²/s) 56.0 56.5 58.3 100° C. Kinematic Viscosity (mm²/s) 9.07 9.10 9.31 Viscosity Index (—) 142 141 140 Friction Test (after one cycle) Kinematic Friction Coefficient (μ0) 0.136 0.128 0.141 Kinematic Friction Coefficient (μd) 0.136 0.131 0.136 Friction Coefficient Ratio (μ0/μd) 1.000 0.977 1.037 Friction Test (after 100 cycles) Kinematic Friction Coefficient (μ0) 0.131 0.124 0.133 Kinematic Friction Coefficient (μd) 0.133 0.126 0.123 Friction Coefficient Ratio (μ0/μd) 0.985 0.984 1.081 Friction Test (after 500 cycles) Kinematic Friction Coefficient (μ0) 0.138 0.136 0.135 Kinematic Friction Coefficient (μd) 0.144 0.144 0.133 Friction Coefficient Ratio (μ0/μd) 0.958 0.944 1.015 Friction Test (after 1000 cycles) Kinematic Friction Coefficient (μ0) 0.143 0.141 0.136 Kinematic Friction Coefficient (μd) 0.144 0.149 0.136 Friction Coefficient Ratio (μ0/μd) 0.993 0.946 1.000 Friction Test (after 3000 cycles) Kinematic Friction Coefficient (μ0) 0.147 0.144 0.135 Kinematic Friction Coefficient (μd) 0.152 0.150 0.137 Friction Coefficient Ratio (μ0/μd) 0.967 0.960 0.985 Friction Test (after 5000 cycles) Kinematic Friction Coefficient (μ0) 0.147 0.147 0.133 Kinematic Friction Coefficient (μd) 0.154 0.154 0.140 Friction Coefficient Ratio (μ0/μd) 0.955 0.955 0.950

The results in Table 1 confirm that the lubricating oil compositions for industrial machines of this embodiment containing the base oil (A) and the acylglycerol (B) all had a friction coefficient ratio of 1 or less in all friction tests, that is, the lubricating oil compositions exhibit excellent brake squeal preventing performance from initial stages and for a long period of time. In addition, it is also confirmed that the lubricating oil composition for industrial machines of this embodiment further containing the amine compound (C) has a smaller friction coefficient ratio than the lubricating oil composition of Example 1 and expresses more excellent brake squeal preventing performance.

On the other hand, it is confirmed that the lubricating oil composition of Comparative Example 1 not containing the acylglycerol (B) had a friction coefficient ratio of 1 or less in the friction test (1000 cycles or more), and the comparative lubricating oil composition could exhibit brake squeal preventing performance in a long term, but in the friction test (after 1 cycle, after 100 cycles, and after 500 cycles), the friction coefficient ratio of the composition was more than 1, and the composition could not express sufficient brake squeal preventing performance in relatively early stages.

INDUSTRIAL APPLICABILITY

The lubricating oil composition for industrial machines of this embodiment is a lubricating oil composition having especially excellent brake squeal preventing performance. The lubricating oil composition for industrial machines of this embodiment and the lubrication method using the composition are, for example, used for general industrial machines such as agricultural machines, construction machines and transporting machines, and are favorably used for industrial machines equipped with a transmission (gear), a hydraulically actuated part and the like. In particular, the lubricating oil composition and the lubrication methods are favorably used for industrial machines equipped with a transmission (gear), a hydraulically actuated part and a wet brake, for example, for construction machines such as hydraulic power shovels, crane vehicles and bulldozers, and transporting machines such as dumper trucks, forklifts, shovel loaders and rough terrain haulers. 

1: A lubricating oil composition for industrial machines, the composition comprising: (A) a base oil (A); and (B) an acylglycerol (B) represented by the following general formula (1):

wherein: R¹¹, R¹², and R¹³ each independently represent an acyl group represented by —C(═O)R¹⁴, or a hydrogen atom; at least any of R¹¹, R¹², and R¹³ is the acyl group; R¹⁴ represents a monovalent hydrocarbon group having 12 or more and 30 or less carbon atoms; and when a plurality of the acyl groups is present, R¹⁴'s in the acyl groups may be the same or different. 2: The lubricating oil composition for industrial machines according to claim 1, wherein a content of the acylglycerol (B) based on the total amount of the composition is 0.01% by mass or more and 2.5% by mass or less. 3: The lubricating oil composition for industrial machines according to claim 1, further comprising: (C) an amine compound (C) represented by the following general formula (2):

wherein: R²¹ represents a hydrogen atom, or a monovalent hydrocarbon group having 12 or more and 30 or less carbon atoms; R²² and R²³ each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 or more and 5 or less carbon atoms; and at least one of R²¹, R²², and R²³ is a hydrocarbon group. 4: The lubricating oil composition for industrial machines according to claim 3, wherein a content of the amine compound (C) based on the total amount of the composition is 0.01% by mass or more and 2.5% by mass or less. 5: The lubricating oil composition for industrial machines according to claim 1, which has a total nitrogen atom content of 500 ppm by mass or more and 2,000 ppm by mass or less based on the total amount of the composition. 6: The lubricating oil composition for industrial machines according to claim 1, wherein: the acylglycerol (B) is a monoacylglycerol represented by the general formula (1) where any one of R¹¹, R¹², and R¹³ is an acyl group represented by —C(═O)R¹⁴; R¹⁴ is an alkyl or alkenyl group having 12 or more and 30 or less carbon atoms; and any two of the other R¹¹, R¹², and R¹³ are hydrogen atoms. 7: The lubricating oil composition for industrial machines according to claim 3, wherein: the amine compound (C) is an amine represented by the general formula (2) where R²¹ is an alkyl or alkenyl group having 12 or more and 30 or less carbon atoms; and R²² and R²³ are hydrogen atoms. 8: The lubricating oil composition for industrial machines according to claim 1, which has a kinematic viscosity at 40° C. of 30 mm²/s or more and 70 mm²/s or less. 9: The lubricating oil composition for industrial machines according to claim 1, wherein the industrial machines are those equipped with a transmission, a hydraulically actuated part and a wet brake. 10: The lubricating oil composition for industrial machines according to claim 1, wherein the industrial machines are transporting machines. 11: A lubrication method, comprising lubricating an industrial machine with the lubricating oil composition of claim
 1. 12: The lubrication method according to claim 11, wherein lubricating of the industrial machine includes lubricating at least one of a transmission, a hydraulically actuated part and a wet brake contained in the industrial machine. 